Epigenetic Regulation of Medulloblastoma

髓母细胞瘤的表观遗传调控

• 批准号: 8287654
• 负责人: LAURIE L JACKSON-GRUSBY
• 金额: $ 35.02万
• 依托单位: BOSTON CHILDREN'S HOSPITAL
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-08 至 2014-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8287654
• 关键词: Address; Alleles; Animals; Awareness; Biological Assay; Brain Neoplasms; Cancer Etiology; Cellular Structures; Childhood; Childhood Brain Neoplasm; Chromosomal Instability; DNA; DNA Methylation; DNA Methylation Inhibition; DNA Methyltransferase; DNA Modification Methylases; Dependence; Disease; Embryonic Development; Epigenetic Process; Event; Fibroblasts; Gene Silencing; Genes; Genetic; Genomics; Goals; Health; Human; Intestinal Neoplasms; Kinetics; Knowledge; Lead; Long-Term Effects; Maintenance; Malignant Neoplasms; Malignant neoplasm of brain; Mediating; Methylation; Modeling; Mus; Mutate; Mutation; Oncogene Deregulation; Pathologic; Pathway interactions; Play; Predisposition; Process; Property; Protein p53; Regulation; Risk; Role; Somatic Cell; Stem cells; TP53 gene; Testing; Therapeutic; Tumor Stem Cells; Tumor Suppressor Genes; Tumor Tissue; cancer risk; cancer stem cell; cancer type; cell growth regulation; cohort; demethylation; embryonic stem cell; genome-wide; imprint; in vivo; insight; medulloblastoma; mouse model; mutant; pluripotency; prevent; promoter; self renewing cell; self-renewal; stem cell population; therapeutic target; tumor; tumor initiation; tumor progression; tumorigenesis

DESCRIPTION (provided by applicant): The overarching goal of this project is to understand two important aspects of epigenetic control during medulloblastoma formation, namely the difference between cancer stem cells and bulk tumor, and the role of DNA methylation dependent gene silencing in tumor progression. Our experimental rationale that connects these two questions is an observation we made that normal mouse embryonic stem cells do not require the sole maintenance DNA methyltransferase Dnmt1, whereas all known somatic cells tested require this gene for survival. The increasing awareness that pluripotency genes, those genes important for embryonic stem cell self-renewal, may play an important functional role in cancer stem cells encourages us to test the importance of this pathway in brain tumor stem cells derived from medulloblastoma. To approach this question, we are utilizing a mouse model harboring mutations in two tumor suppressor genes, Ptch and p53, that when mutated lead to a highly penetrant and lethal medulloblastoma. To examine the role for epigenetic control in cancer stem cells we will first characterize Ptch-P53 medulloblastomas to determine whether they contain a self- renewing cancer stem cell population. We will then test whether the self-renewing cells within these medulloblastomas are Dnmt1 dependent like other somatic cells or are Dnmt1 independent like embryonic stem cells. To address the role of epigenetic silencing, we will utilize a viable hypomorphic allele of Dnmt1 and ask whether genomic DNA hypomethylation induces or suppresses medulloblastoma formation. Depending on tumor context, Dnmt1 hypomorphic mice have revealed important roles for DNA hypomethylation in promoting chromosomal instability and alternatively in preventing aberrant gene silencing. We will determine whether chromosomal or epigenetic mechanisms prevail in medulloblastoma progression using a genetic approach with Dnmt1 hypomorphic mice. Finally, we have recently demonstrated that transient demethylation in embryonic stem cells leads to global loss of imprinting, and loss of p53 expression in derived mouse fibroblasts through an unknown mechanism. We have derived ES cells from medulloblastoma prone Ptch mice in order to carry out transient demethylation in stem cells and test whether epigenetic mechanisms lead to loss of p53 and promote medulloblastoma tumor progression in vivo. These results will extend prior results that global loss of imprinting can promote tumorigenesis, and provide a model to dissect the mechanism through which transient epigenetic changes exert long term effects on cell growth regulation, and tumor predisposition in vivo. PUBLIC HEALTH RELEVANCE: This proposal tests four hypotheses regarding the contribution of epigenetic alterations to medulloblastoma initiation and progression. We ask are cancer stem cells similar to embryonic stem cells in their lack of dependence on the DNA methyltransferase Dnmt1, and does global transient demethylation promote cancer by potentiating cancer stem cell expansion? We test the contribution of epigenetic alterations by asking does gene silencing contribute to tumor initiation or progression, and are imprinted genes a key functional class of epigenetic targets that become deregulated in these pediatric brain tumors? Answers to these questions should yield insight into the origins of the most common pediatric brain tumor, and will likely impact a broader understanding of cancer epigenetics.

描述（由申请人提供）：该项目的总体目标是了解髓母细胞瘤形成过程中表观遗传控制的两个重要方面，即癌症干细胞和大块肿瘤之间的差异，以及DNA甲基化依赖的基因沉默在肿瘤进展中的作用。我们将这两个问题联系起来的实验原理是我们观察到正常小鼠胚胎干细胞不需要唯一的DNA甲基转移酶Dnmt 1，而所有已知的体细胞都需要这个基因才能生存。越来越多的人意识到，多能性基因，这些基因对胚胎干细胞的自我更新很重要，可能在癌症干细胞中发挥重要的功能作用，这促使我们在髓母细胞瘤来源的脑肿瘤干细胞中测试这一途径的重要性。为了解决这个问题，我们正在利用一个小鼠模型窝藏突变的两个肿瘤抑制基因，Ptch和p53，当突变导致一个高度渗透和致命的髓母细胞瘤。为了检查癌症干细胞中表观遗传控制的作用，我们将首先表征Ptch-P53髓母细胞瘤以确定它们是否含有自我更新的癌症干细胞群体。然后，我们将测试这些髓母细胞瘤中的自我更新细胞是否像其他体细胞一样依赖Dnmt 1，或者像胚胎干细胞一样不依赖Dnmt 1。为了解决表观遗传沉默的作用，我们将利用Dnmt 1的一个可行的亚型等位基因，并询问基因组DNA低甲基化是否诱导或抑制髓母细胞瘤的形成。根据肿瘤的情况，Dnmt 1亚型小鼠揭示了DNA低甲基化在促进染色体不稳定性和防止异常基因沉默中的重要作用。我们将确定是否染色体或表观遗传机制占主导地位的髓母细胞瘤的进展，使用遗传方法与Dnmt 1亚型小鼠。最后，我们最近已经证明，在胚胎干细胞的瞬时去甲基化导致全球损失的印记，并通过一个未知的机制在衍生的小鼠成纤维细胞中的p53表达的损失。我们已经从有髓母细胞瘤倾向的Ptch小鼠中获得ES细胞，以便在干细胞中进行瞬时去甲基化，并测试表观遗传机制是否导致p53丢失并促进髓母细胞瘤的体内进展。这些结果将扩展先前的结果，即印记的整体损失可以促进肿瘤发生，并提供了一个模型，以解剖短暂的表观遗传变化对细胞生长调节和体内肿瘤易感性产生长期影响的机制。公共卫生相关性：该建议测试了四个假设，关于表观遗传改变的髓母细胞瘤的启动和进展的贡献。我们问，癌症干细胞是否与胚胎干细胞相似，缺乏对DNA甲基转移酶Dnmt 1的依赖性，以及全局瞬时去甲基化是否通过增强癌症干细胞扩增来促进癌症？我们通过询问基因沉默是否有助于肿瘤的发生或进展来测试表观遗传改变的贡献，以及印记基因是否是在这些儿科脑肿瘤中变得失调的表观遗传靶点的关键功能类别？这些问题的答案应该会让我们深入了解最常见的儿科脑肿瘤的起源，并可能会影响对癌症表观遗传学的更广泛理解。